Sleep Boosts Immunity

By Maria M. Hadjimarkou, PhD. Lecturer School of Psychology University of Sussex

The past three years have changed the way we live, the way we behave and the way we think about our lives. We have become more aware of our vulnerability to diseases caused by infectious agents. The coronavirus SARS-CoV-2 is a virus like many others, that invades our bodies, replicates itself and spreads by infecting more people. So many of us have been infected and will probably be infected again, with future variants. The response of each of us to the virus varied tremendously, from completely asymptomatic to mild to severe. Unfortunately, many have died. During the peak of the epidemic, many have searched for remedies like vitamins and minerals, to boost their immune system. It would have been helpful to know that simply by sleeping well, we are contributing massively to our immune system’s ability to fight off disease. Did you know that sleep is an ally of the immune system? Read further to get a glimpse of how this may be happening and what research shows.

Our immune system is our body’s defence mechanism against invaders. It is generally divided into two types; the innate, which can be considered as the default immune system that offers quick but general (non-specific) protection against infectious agents, mainly by eating them up (phagocytosis). The other type is the adaptive immune system, which is slower to respond but more sophisticated and more specific in its work. Part of the adaptive immune system’s task is to correctly identify the specific pathogens and to produce custom-made antibodies, cells that will target pathogens specifically and eliminate them. In addition, the adaptive immune system creates a ‘library’ of the pathogens it has encountered so that it can be ready for defence if the same invader happens to attack again, also known as the immune system’s memory. The cells that specialize in this kind of dedicated work are primarily B cells and T cells, leukocytes (white blood cells) produced in bone marrow.

It is becoming evident that those of us who get a good night’s sleep are more likely to have a well-functioning immune system compared to those that do not sleep well and sleep very little (6h or less). The recommended time for sleep is about 8 hours (7-9 hrs) every night for adults and even more for children and teenagers. In studies where people were administered a virus in a controlled environment and had their sleep monitored before and after the infection, found that those who slept fewer hours or had disturbed sleep were more likely to get sick from the virus whereas those sleeping the recommended time were more resistant.

Specifically, in a study by Cohen et al 2009, healthy people were asked about their sleep up to 14 days prior to quarantining themselves in a controlled environment. They were subsequently given nasal drops that contained rhinovirus, a virus that causes the common cold and were monitored for the next five days for symptoms of sickness. There was a strong association between prior sleep and the development of a cold, so that those with less than 7 hours of sleep the night before, were almost three times more likely to get sick than those with 8 hours of sleep or more. Also, those with less sleep efficiency (time asleep divided by the time in bed), were more than five times more likely to develop a cold than those with better sleep efficiency.

This finding was replicated in a similar study where instead of relying on subjective measures such as people’s reports about their sleep, the experimenters monitored prior sleep for seven days, using more objective measures such as actigraphy in addition to sleep diaries. Again, they found that those with less than 6 hours of sleep were more susceptible and more likely to have developed a cold. Similar evidence has emerged during the pandemic, with studies finding that those with poor quality sleep the month prior to infection with covid-19, were more likely to be more severely ill, stay in the hospital longer and importantly, more likely to require intensive care compared to those that slept well.

Besides finding that sleep helps our ability to resist illness upon infection, studies show that sleep contributes to the build-up of our immunity following vaccination, which is something that we were all striving for, for the past couple of years. The first study to demonstrate this was in 2003. In this study, half of those participating were allowed to sleep, and the other half were kept awake the night after a hepatitis A vaccine. Antibodies and other indicators of immune system function were monitored for the next 28 days. They found that those kept awake the night after their vaccination, had significantly fewer antibodies compared to those who slept. After four weeks, when antibody levels were expected to peak, those who had slept the night after getting vaccinated had two times more antibodies compared to those who didn’t. Following this study, several others have found that lack of sleep around the time of vaccination has a significant impact on the number of antibodies produced in the short- and longer-term. A more recent study published in 2021 monitored sleep before and after vaccination with the influenza vaccine and indicated that the two nights preceding vaccination were the most important for immunity, even four months later. Although up to this point there are no published studies on covid-19 vaccines and sleep and immunity specifically, we can assume that it will not be any different compared to the other vaccines that have been studied so far.

Sleep enhances the immune system’s memory even a year later with greater numbers of T-helper cells (Th) cells and antibodies against the targeted virus. More specifically, studies highlight the importance of slow-wave-sleep (SWS) in this process which has implications for our lifestyle and bedtime habits. During this deep stage of sleep, the white blood cells that normally circulate in the bloodstream withdraw from circulation and accumulate in the lymph nodes where they are presented with new antigens, new infectious particles that have entered our bodies, in order to launch a targeted immune response. Changes in the levels of growth hormone, a hormone secreted during SWS in the early part of the night increases dramatically along with prolactin, in order to enhance this adaptive immune response. Those who sleep sufficiently have greater levels of these hormones during this time compared to those that don’t sleep and their antibodies are also greater, in some cases four times greater, than those who did not sleep.
Thus, sleep and the immune system are interconnected. Several chemicals released during infection called cytokines also enhance non-REM (NREM) sleep, and more specifically SWS. Recently, a novel gene has been identified in fruit flies (drosophila melanogaster) by researchers using a genetic approach. This new gene called nemuri codes for a protein that induces sleep in flies, but it also has antimicrobial activity, linking sleep and the immune system even further.

Given that SWS takes place mostly in the early part of the night, these findings highlight the importance of going to bed early, in order not to miss that important part of our sleep. As a nation, we have all displayed the desire to resist and fight the virus on a personal and global level. However, the importance of sleep on our immune response has not received the appropriate attention. The evidence reviewed here, suggests that we are less susceptible to getting sick upon infection and that vaccinations can be more effective if we sleep well, especially around the time of vaccination. Given that in the autumn we may need to have another round of vaccinations against covid-19, influenza or other viruses, this is useful information to have.

Reference:
Besedovsky L, Lange T, Haack M. The Sleep-Immune Crosstalk in Health and Disease. Physiol Rev. 2019 Jul 1;99(3):1325-1380.